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When the driver pressed the brake pedal, why doesn't the vehicle disengage the throttle? I remember when this happened and many demonstrations were done that ev

When the driver pressed the brake pedal, why doesn't the vehicle disengage the throttle? I remember when this happened and many demonstrations were done that even if you were pressing the pedal to the floor, the brake disengages the throttle and brings the car to a stop.

HPsquared 4y ago
Ironically on a car with vacuum assisted brakes and no mechanical vacuum pump, it's the other way round: when full throttle, there is no vacuum available and (after a few uses) the brakes become substantially weaker. That's on naturally-aspirated engines without a software override, anyway.
- 0xfeba 4y ago
  But they'll typically have a check valve good for one assist. Assuming you press once and only once and *hard*, they will win. But that's a big assumption to make for people panicking.
  - jandrese 4y ago
    Also, the general guidance for someone who thinks their brakes are failing is to pump them to try to build pressure. In this case that guidance is the exact opposite of what you should do. The guidance is for a different but more common failure mode: brake line rupture. The correct solution to a runaway engine is to slap the car into neutral and then apply brakes and pull over if necessary. But that's not something most driving schools teach nor is it something your average person will practice.
  - throwaway0a5e 4y ago
    >But they'll typically have a check valve good for one assist 2-3 in practice.
0xfeba 4y ago
Some do (at least now) but there's no standard/regulation for it.
justoreply 4y ago
According to this podcast, in order to stop the car you just need to brake, as brakes are always more powerful than the engine https://www.pushkin.fm/episode/blame-game/ https://www.pushkin.fm/episode/blame-game/
- camhenlin 4y ago
  > brakes are always more powerful than the engine That's really not true at all. Generally, as braking systems pick up heat, they become continually less and less efficient at slowing the car down and will eventually stop working entirely. This will be especially true when fighting against an engine running at wide open throttle. It's called brake fade.
  - BoorishBears 4y ago
    Brake fade is a thing, but firm deliberate use of the brakes would slow the car down enough for you to turn it off well before your brake fluid was cooked. The problem is having the presence of mind to do that when confronted with such an unusual situation
  - hatsunearu 4y ago
    In my experience brake fade doesn't kick in until an inordinate amount of heat gets generated (think like full send down a steep mountain for tens of minutes) or you're doing something stupid (like full send down a steep mountain for tens of minutes)
- InitialLastName 4y ago
  Malcolm Gladwell has a long history of taking every opportunity available to use misleading interpretations of evidence to justify his fables [0 for a notable example]. I would take anything he puts an "always" behind with a very large (boulder-sized) grain of salt. [0] http://askakorean.blogspot.com/2013/07/culturalism-gladwell-and-airplane.html http://askakorean.blogspot.com/2013/07/culturalism-gladwell-...
- jandrese 4y ago
  I think the issue is that a runaway engine will lose vacuum which makes the brake boosters ineffective.
BoorishBears 4y ago
Brake Override function was also running on that CPU
- salawat 4y ago
  Which still requires the assumption of well behaving control flow. Most brakes don't actually lockout engine operation, because there are cases where you want the engine to rev while the brake is applied. Just because at first blush it seems the use case is pointless, doesn't mean it is.
  - BoorishBears 4y ago
    Not sure what you're trying to say, the Camry did have a Brake Override function and it was running on the same CPU, that's not sarcasm. You think the Camry was designed for track duty?

HPsquared 4y ago

Ironically on a car with vacuum assisted brakes and no mechanical vacuum pump, it's the other way round: when full throttle, there is no vacuum available and (after a few uses) the brakes become substantially weaker. That's on naturally-aspirated engines without a software override, anyway.

0xfeba 4y ago
But they'll typically have a check valve good for one assist. Assuming you press once and only once and *hard*, they will win. But that's a big assumption to make for people panicking.
- jandrese 4y ago
  Also, the general guidance for someone who thinks their brakes are failing is to pump them to try to build pressure. In this case that guidance is the exact opposite of what you should do. The guidance is for a different but more common failure mode: brake line rupture. The correct solution to a runaway engine is to slap the car into neutral and then apply brakes and pull over if necessary. But that's not something most driving schools teach nor is it something your average person will practice.
- throwaway0a5e 4y ago
  >But they'll typically have a check valve good for one assist 2-3 in practice.

0xfeba 4y ago

Some do (at least now) but there's no standard/regulation for it.

justoreply 4y ago

According to this podcast, in order to stop the car you just need to brake, as brakes are always more powerful than the engine https://www.pushkin.fm/episode/blame-game/ https://www.pushkin.fm/episode/blame-game/

camhenlin 4y ago
> brakes are always more powerful than the engine That's really not true at all. Generally, as braking systems pick up heat, they become continually less and less efficient at slowing the car down and will eventually stop working entirely. This will be especially true when fighting against an engine running at wide open throttle. It's called brake fade.
- BoorishBears 4y ago
  Brake fade is a thing, but firm deliberate use of the brakes would slow the car down enough for you to turn it off well before your brake fluid was cooked. The problem is having the presence of mind to do that when confronted with such an unusual situation
- hatsunearu 4y ago
  In my experience brake fade doesn't kick in until an inordinate amount of heat gets generated (think like full send down a steep mountain for tens of minutes) or you're doing something stupid (like full send down a steep mountain for tens of minutes)
InitialLastName 4y ago
Malcolm Gladwell has a long history of taking every opportunity available to use misleading interpretations of evidence to justify his fables [0 for a notable example]. I would take anything he puts an "always" behind with a very large (boulder-sized) grain of salt. [0] http://askakorean.blogspot.com/2013/07/culturalism-gladwell-and-airplane.html http://askakorean.blogspot.com/2013/07/culturalism-gladwell-...
jandrese 4y ago
I think the issue is that a runaway engine will lose vacuum which makes the brake boosters ineffective.

BoorishBears 4y ago

Brake Override function was also running on that CPU

salawat 4y ago
Which still requires the assumption of well behaving control flow. Most brakes don't actually lockout engine operation, because there are cases where you want the engine to rev while the brake is applied. Just because at first blush it seems the use case is pointless, doesn't mean it is.
- BoorishBears 4y ago
  Not sure what you're trying to say, the Camry did have a Brake Override function and it was running on the same CPU, that's not sarcasm. You think the Camry was designed for track duty?